Metal plate type of arc-extinguishing device



l.. L. BAIRD April 22, 1969 METAL PLATE TYPE OF ARC-EXTINGUISHING D EVICE Filed April 5. 1966 A TTORNEY United States Patent O U.S. Cl. 200-144 5 Claims ABSTRACT F THE DISCLOSURE An arc chute comprising spaced-apart sidewalls of insulating material `for enclosing the arc. Spaced-apart metal plates between the sidewalls are disposed across the path of the arc to chop the arc into series-related arclets between the plates. Each plate contains a channel that extends from its exposed edge in a direction away from the arc-initiation region. The sidewalls of each channel are located to intercept arc-liberated metal particles projectedfin straight line paths from the bottom of the channel toward said insulating sidewalls. V-notches in the exposed edges of the plates direct the arc onto the plates in a location between the channel sidewalls.

This invention relates to an arc-extinguishing device, or an are chute, of a type that comprises spaced sidewalls of insulating material and metal plates extending between the sidewalls for chopping an arc into a family of seriesrelated arclets.

In certain arc chutes of this type, it has been found that a thin coating of metal particles will app-ear along the insulating sidewalls after a high current interruption. This metal coating is objectionable because it can cause eX- cessive leakage currents to ilow through the chute or can cause a dieletcric breakdown along the surface of the sidewalls. This metal coating is believed to result from vaporization of the metal plates and arcing contacts by the high temperature arc. The arc-generated metal vapors are projected in all directions from the arcing region and condense on adjacent surfaces, thus forming a coating on these surfaces.

An object of my invention is to provide simple and inexpensive means for protecting the insulating sidewalls of the arc chute from such metal deposition.

Another object is to provide protective means of the above nature which consumes very little space and does not require any substantial reduction in the number of spaced metal plates that can be litted into an arc chute of a given size.

For preventing an are from reestablishing across the rear edge of the metal plates after it is rst extinguished, insulating barrier plates, substantially coplanar with certain of the metal plates, have heretofore been provided at the rear edges of the metal plates. For these barrier plates to ybe eective, it is important that they t tightly against the read edge of the metal plates so that there is no space available in which the arc can restrike.

Another object of my invention is to shape the metal plates in such a manner that they can act to protect the sidewalls against vapor deposition, yet without impairing the desired tight t between the metal plates and the insulating barrier plates.

In carrying out the invention in one form, I provide means for initiating an are in an arc-initiation region and a pair of spaced-apart sidewalls of insulating material for enclosing the arc. A plurality of spaced-apart metal plates spanning the sidewalls are disposed across the path of the arc, with the exposed edges of the plates facing the arc-initiation region. The arc is moved transversely of its length into engagement with these ex- 3,440,378 Patented Apr. 22, 1969 posed edges, thereby chopping the arc into a family of series-related arclets. At least some of the metal plates each contain a channel that extends from the exposed edge of the plate in a direction away from said arcinitiation region. Each of the channels has a bottom wall and sidewalls at opposite edges of the bottom wall. Each channel has its sidewalls located to intercept arc-liberated metal particles projected in straight line paths from the bottom of the channel toward said insulating sidewalls. At least some of the channeled metal plates each contain a generally V-shaped notch in the exposed edge of the plate with the V-shaped notch being located in a position between the channel sidewalls. The bottom of the channels in adjacent metal plates are displaced from the remainder of their respective plates in generally the same direction, with the channeled portions in adjacent metal plates being disposed in generally aligned relationship.

For a better understanding of the invention, reference may be had to the following description taken in conjunction with the accompanying drawing, wherein:

FIG. 1 is a side elevational view, partly in section, showing an arc chute embodying one form of my invention.

FIG. 2 is a sectional view along the line 2 2 of FIG. 1.

FIG. 3 is a sectional view along the line 3 3 of FIG. l.

FIG. 4 is a perspective view of one of the metal plates used in the ar-c chute of FIG. 1.

Referring now to FIG. 1, I have shown an electric circuit interrupter comprising contact structure 11 separable to establish an arc and an arc chute 12 for enclosing and extinguishing the arc. Although the contact structure 11 may take any suitable form, as illustrated it comprises a relatively stationary contact member 13 mounted on a current-conducting stud 14 and a cooperating contact arm 15 supported for pivotal movement into and out of circuit making engagement with the stationary contact member 13. In FIG. l the movable contact arm 15 is shown in its open-circuit position.

The actuating means for moving the contact arm 15 during circuit making and interrupting operations is omitted from the drawing for the sake of clarity. A more detailed disclosure of the schematically illustrated contact structure 11 is believed unnecessary for a full understanding of my invention.

The arc chute or extinguisher 12 comprises a pair of spaced sidewalls 18 and 19 of electric insulating material. Preferably, the side walls are made of a ceramic material, such as porcelain, which is conveniently formed in the desired shape. Each side wall 18, 19 is substantially the mirror image of the other, and both are provided at their right and left-hand ends, as viewed in FIG. l, with abutting transverse portions which determine the spacing therebetween. The whole assembly is held together by suitable means, such as bolts 23 extending transversely through the abutting portions of the arc chute.

When an arc is established between the contacts 13 and 15, it is driven upwardly into the arc chute 12 in a conventional manner. In this regard, the left hand terminal of the arc moves upwardly into the arc chute 12 along a metal arc runner 16, which is electrically connected to the contact 13. The right hand arc terminal remains attached to the movable Contact 15 until a predetermined gap is established between the contacts 13 and 15, after which this right hand arc terminal transfers to an arc runner (not shown) at the right hand edge of the chute and then moves upwardly into the chute.

Spanning the side walls 18 and 19` above the arc-initiation region are a plurality of spaced-apart solid metal plates 29 which extend transversely across the path of the arc drawn between contacts 13 and 15. As the arc moves upwardly into the arc chute 12, it engages the exposed lower edges of plates 29, and the plates chop the arc into a family of series-related arclets which are subsequently deionized and extinguished as they move within the spaces between the adjacent plates.

For facilitating entry of the arc onto the metal plates 29, the exposed lower edges of plates 29 are provided with notches 30 of generally V-shaped conguration. The vertex of each of these V-shaped notches 30 points away from the arc-initiation region.

The spaced-apartv metal plates 29 are held in place by means of appropriate pairs of vertical grooves 31 respectively provided in the opposing surfaces of the ceramic sidewalls 18 and 19, each pair of grooves receiving the opposite ends of one plate. Reduced depth portions of some of the grooves 31 extend below the metal plates 29, as can be seen in FIG. l, in order to increase the length of the electrical creepage path over this part of the surface of the sidewalls.

The arc products generated in the arc chute 12 during a circuit-interrupting operating are exhausted through an outlet 33 provided by an opening between the sidewalls 18 and 19 at the upper end of the chute. The hot arc products pass upward from the area of the metal plates 29 through a mufer disposed across the outlet 33. The muflier 34, which comprises a plurality of serpentine strips of perforated metal, rapidly cools the arc products as they impinge against it. Thus suppresses flame-emission from the arc chute 12 during circuit interruption and prevents conduction of flashover to any grounded metal parts which may be located closely above the chute.

In prior arc chutes having metal plates and ceramic sidewalls, it has been found that a thin coating of metal particles appears along the sidewalls after a high current interruption. This metal coating is objectionable because itcan allow excessive leakage currents to flow through the chute or can lead to a dielectric breakdown along the surface of the sidewalls.

,For protecting the insulating sidewalls 18, 19 from this metal deposition, I provide each of the arc-chopping metal plates 29 with a channel 40 that extends from its exposed lower edge toward its top edge, i.e., in a direction away from the arc-initiation region. Referring to FIG. 3, this channel 40 may be thought of as comprising a bottom wall 41 and a pair of sidewalls 42 at opposite edges of the bottom wall. Each channel 40 has its sidewalls 42 located to intercept arc-generated metal vapors that are projected from the bottom wall 41 of the channel toward the insulating sidewalls 18, 19. A large portion of these vapors condense on the channel sidewalls 42 before they can reach the insulating sidewalls, and thus metal deposition on the insulating sidewalls is drastically reduced. It appears that a large percentage of the arc-generated vapors are projected in straight line paths from the bottom of the channel toward the insulating sidewalls, and the channel sidewalls are in a position to intercept and condense such vapors.

Another feature that facilities interception of the metal vapors is that the adjacent plates 29 are disposed close together with their channel portions in generally aligned relationship, as will be apparent from FIG. 3. This aligned relationship of the closely-spaced channeled plates 29 presents a tortuous path to the metal vapors traveling toward the insulating sidewalls and enables the plate with the convex configuration facing the arcing space, as well as the opposed plate, to intercept a substantial amount of the metal vapors generated bythe arc.

=I have found that the metal coating results primarily from a high current arc vaporizing the metal plates along the edges of the V-shaped notch 30, particularly near the vertex of the V-notch. Upward motion of the arc seems to be delayed slightly when the arc is at the edge of the plate in the vertex region, and it is during this delay period that most of the metallic vapors are generated by the arc. Once the arc has been chopped into a pair of arclets by the plate, the terminals of the arclets move about rapidly on the plate and generate a much lower quantity of metal vapors.

If the arcs moved ontothe metal plates 29 in locations immediately adjacent the insulating sidewalls 18, 19, then the channel sidewalls 42 could do little to protect the insulating sidewalls against metal deposition since the channel sidewalls would not be interposed between the are and the insulating sidewalls 18, 19. I overcome this problem by preventing the arc from moving onto the metal plates immediately adjacent the insulating sidewalls 18, 19. More specifically, the V-shaped notch 30 acts to force the arc to move onto the metal plate near the vertex of the V, and thus the channel sidewalls 42 are in a position to intercept the vapors that are generated by the arc during the interval of maximum arc erosion.

In a preferred form of my invention, the channel in each plate is shaped so that it has a depth that gradually decreases to Zero before the upper edge of the plate is reached. Thus, the plate in the region adjacent its upper edge is substantially flat. The absence of channel sidewalls 42 in this upper region does not significantly detract from the protection afforded the insulating sidewalls against metal-deposition. This is the case because only small amounts of metal vapor are generated by the arclets after they have passed beyond the exposed lower edge of the plate and are moving around on the plate.

At the upper edge of alternate metal plates 29, barrier plates 50 of insulating material are provided. These barrier plates 50 serve to prevent the reestablishrnent or restriking of an arc across the tops of the metal plates 29. To assist the barrier plates S0 in performing this function, it is important that the lower edge 51 of the barrier plate be substantially contiguous with and tightly fitted against the upper edge of the metal plate 29. This eliminates any open path across the top of the metal plates 29 through which the arc could reestablish.

One factor that contributes to a good seal between the upper edge of the metal plate 29 and the lower edge of the insulating barrier plate 50 is the fiat configuration of the metal plate adjacent its upper edge. Because the upper region of the metal plate is at, it can be disposed in contiguous and substantially coplanar relationship with the flat barrier plate, thus eliminating any open space `between the two plates.

Referring to FIG. 3, which is a cross-sectional view taken along a plane containing line 3-3 and extending normal to the insulating sidewalls and transversely of the bottom wall of the channels, it is to be noted that the presence of the channels 40 in the metal plates 29 does not necessitate any appreciably larger spacing between the plates 29 at their transverse edges or elsewhere. Even though the presence of the channel 40 in a given plate results in an embossment on the opposite face ofthe plate, the channel 40 in the adjacent plate receives this embossment in generally aligned relationship, and there is no decrease in plate-spacing around the walls of the embossment. The fact that the sidewalls 42 of the channel are disposed at an obtuse angle to the bottom Iwall 41 is another factor permitting a generally aligned relationship of the channels without appreciably reducing the platespacing.

While I have shown and described a particular ernbodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects; and I, therefore, intend in the appended Claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric circuit interrupter comprising:

(a) means for initiating an arc in an arc-initiation region,

(b) a pair of spaced-apart sidewalls of insulation material for enclosing the arc,

(c) a plurality of spaced-apart metal plates spanning the sidewalls and disposed across the path of the arc with exposed edges of the plates facing said arc-initiation region,

(d) means for moving the arc transversely of its length into engagement with said exposed edges of the plates thereby chopping the arc into a family of series-related arclets,

(e) immediately adjacent ones of said metal plates each containing a channel that extends from the exposed edge of the plate in a direction away from said arcinitiation region, each channel having a bottom wall and sidewalls at opposite edges of the bottom wall,

(f) each of said channels having its sidewalls located to intercept arc-liberated metal particles projected in straight line paths extending generally normal t0 the insulating sidewalls from the bottom of the channel toward said insulating sidewalls,

(g) at least some of said channelled metal plates each containing a generally V-shaped notch in the exposed edge of said plate, said V-shaped notch being located in a position between said channel-sidewalls, and

(h) the bottom wall of the channels in said immediately adjacent metal plates being displaced from the remainder of their respective plates in generally the same direction, with the channelled portions in said immediately adjacent plates being disposed in generally aligned relationship, as viewed in a cross-section plane extending through said plates normal to said insulating sidewalls and transversely of the bottom wall Of the channels.

2. The circuit interrupter of claim 1 in combination with insulating bale plates abutting the rear edge of some of said metal plates and disposed in generally coplanairelationship with their associated metal plates, the metal plates that are in generally coplanar relationship with insulating baille plates -being generally flat adjacent their rear edge and having their respective channels of gradually decreasing depth as the channel extends .away from the exposed edge of the metal plate.

3. The circuit interrupter of claim 1 in which some of said channels are of gradually decreasing depth as they extend away from the exposed edge of the plates.

4. An electric circuit interruptor comprising:

(a) means for initiating an arc in an arc-initiation region,

(b) .a -pair of spaced-apart sidewalls of insulating material for enclosing the arc,

(c) a plurality of spaced-apart metal plates spanning the sidewalls and disposed across the path of the arc rwith exposed edges of the plates facing said .arc-initiation region,

(d) means for moving the are transversely of its length into engagement with said exposed edges of the Iplates thereby chopping the arc into a family of series-related arclets,

(e) immediately adjacent ones of said metal plates each containing a channel that extends from the exposed edge of the plate in a direction away from said arcinitiation region,

(f) each channel having a bottom wall and a sidewall at one edge thereof, l

(g) ,at least some of said channelled metal plates each containing a generally V-shaped notch in the exposed edge of the plate,

(h) said channel sidewall being located between the vertex region of said V-shaped notch and one of said insulating sidewalls so as to be in a position to intercept arc-generated metal particles projected from said vertex region toward said one insulating sidewall, and

(i) the bottom wall of the channels in said immediately adjacent metal plates being displaced from the remainder of their respective plates in generally the same direction, with the channelled portions of said immediately adjacent metal plates being dis-posed in generally aligned relationship, as viewed in a crosssectional plane extending through said plates normal to said insulating sidewalls and transversely of the bottom wall of the channels.

5. The circuit interrupter of claim 4 in combination with insulating baffle plates abutting the rear edge of some of said metal plates and disposed in generally coplanar relationship with their associated metal plates, the metal plates that are in generally coplanar relationship with insulating bathe plates lbeing generally at adjacent their rear edge and having their respective channels of gradually decreasing depth as the channel extends away from the exposed edge of the metal plate.

References Cited UNITED STATES PATENTS 2,236,580 4/1941 Sandin et al. 200-144 2,615,109 10/1952 Favre.

2,934,629 4/ 1960 Bonnefois et al 200-144 3,031,552 4/1962 Stewart.

ROBERT S. MACON, Primary Examiner.

U.S. Cl. X.R. ZOO- 147 

